We're taking a couple of LD trains this summer and I will definitely want to deal with the ceiling vents in the Superliner. Has anyone tried using those magnetic vent covers that go over heating registers? I was thinking they'd be reusable and handier than messing around with cardboard and gaffers tape, but that would require the vents to be ferrous. Anyone know? (Or conversely, anyone know whether this would be a bad/damaging idea?)